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1. A group or set of four.
2. A tetravalent atom, radical, or element.
a. A four-part structure that forms during the prophase of meiosis and consists of two homologous chromosomes, each composed of two sister chromatids.
b. A group of four haploid cells, such as spores, formed by meiotic division of one mother cell.
relating to something that has a group of four